1. Field of the Invention
The present invention relates to improvements in a heat pump type air conditioner applied to a vehicle.
2. Description of the Related Art
Japanese Patent Provisional Publication No. 2-290475 and Japanese Utility Model Provisional Publication No. 2-130808 disclose typical heat pump type air conditioner for an automotive vehicles. Such an air conditioner is provided with a four-way valve for changing refrigerant flow between a heating operation and a cooling operation. Accordingly, during the heating operation an outer heat exchanger is used as a heat absorber, and an inner heat exchanger is used as a heat radiator. On the other hand, during the cooling operation the outer heat exchanger is used as a heat radiator, and the inner heat exchanger is used as a heat absorber.
FIG. 10 shows the heat pump type air conditioner disclosed in Japanese Patent Provisional Publication No. 2-290475. In this heat pump type air conditioner, during a heating operation, a four-way valve 2 is set as indicated by a continuous line in FIG. 10, and refrigerant is circulated as follows: A compressor 1.fwdarw. the four-way valve 2.fwdarw. a first inner heat exchanger 3.fwdarw. a heating heat exchanger 4.fwdarw. a second inner heat exchanger 5.fwdarw.an expansion valve 6.fwdarw. an outer heat exchanger 7.fwdarw. the four-way valve 2.fwdarw. a receiver 8.fwdarw. the compressor 1. Accordingly, the heat of the refrigerant is transmitted to air led by a blower fan 9 and is used for heating a passenger compartment. The heat from an engine 10 is transmitted to the refrigerant through the heating heat exchanger 4 and further transmitted from the refrigerant to air led by a blower fan 11 for heating the passenger compartment. The heat of the air led by a fan 12 is transmitted to the refrigerant through the outer heat exchanger 7.
On the other hand, during the cooling operation, the four-way valve 2 is set as indicated by a dashed line in FIG. 10 and refrigerant is circulated as follows: The compressor 1.fwdarw. the outer heat exchanger 7.fwdarw. the expansion valve 6.fwdarw. the second inner heat exchanger 5.fwdarw. the first inner heat exchanger 3.fwdarw. the four-way valve 2.fwdarw. the receiver 8.fwdarw. the compressor 1. Accordingly, the heat of the refrigerant discharged from the compressor 1 is radiated into the atmosphere by the outer heat exchanger 7. The heat of air led by the blower fans 9 and 11 is transmitted into the refrigerant by the first and second inner heat exchanger 3 and 5. The cooled air is supplied to the passenger compartment.
With such a conventional air conditioner, the absorbed heat amount by the outer heat exchanger 7 is decreased during the heating operation under a condition such that the ambient temperature is low, the automotive vehicle is in running, or it is raining or snowing. Furthermore, if the workload of the compressor 1 is constant, the radiated heat amount from the first and second inner heat exchangers 3 and 5, which is the sum of the heat absorbing amount from the outer heat exchanger 7 and the workload of the compressor 1, is decreased, and the heating capacity of the air conditioner is lowered. Additionally, the lowering of the heating capacity invites the frost to the heat exchanger. This increases a defrost operation and prevents a stable heating operation. Furthermore, since the conventional air conditioner is arranged such that the flow direction of the refrigerant is changed under the cooling and heating operations, it is necessary to change the design of the conduits of the outer and inner heat exchangers 7, 3 and 5 so as to be durable to high temperature and high pressure.
Also, since the conventional air conditioner is arranged to generate heated air for heating by utilizing the waste heat of the engine 10 during the heating operation, this air conditioner can not sufficiently operate if applied to a vehicle which only has small heat source, such as to a solar car or electric vehicle.
Furthermore, since the conventional air conditioner is arranged to select one of the cooling and heating operations on the basis of the difference between a target outlet air temperature and an inlet air temperature to the inner heat exchangers 3 and 5 and can not simultaneously carry out both cooling and heating operations, a dehumidifying heating operation can not be implemented by the conventional air conditioner.
In contrast, another heat pump type air conditioner has been proposed in the U.S. patent application Ser. No. 07/995,096, filed Dec. 22, 1992. The heat pump type air conditioner for a vehicle is arranged as shown in FIG. 11. With this air conditioner, it becomes possible to stably implement air-conditioning operation and to improve air-conditioning performance without being effected by a weather condition. In addition, it becomes possible to implement dehumidifying heating operation. During a heating operation by this air conditioner, a three-way valve 132 is switched as indicated by a continuous line arrow, and therefore the refrigerant is circulated in the air conditioner as follows: A compressor 131.fwdarw. the three-way valve 132.fwdarw. a heat-radiating inner heat exchanger 133.fwdarw. a receiver 136.fwdarw. an expansion valve 134.fwdarw. a heat-absorbing inner heat exchanger 135.fwdarw. the compressor 131. Therefore, air led by a fan blower is cooled and dehumidified by the heat absorbing-inner heat exchanger 135 and then heated by the heat-radiating inner heat exchanger 133 in order to supply conditioned-air for heating into a passenger compartment. On the other hand, during a cooling operation, the three-way valve 132 is switched as indicated by a dashed line arrow, and the refrigerant is circulated in the air conditioner as follows: The compressor 131.fwdarw. the three-way valve 132.fwdarw. an outer heat exchanger 138.fwdarw. a one-way valve 170.fwdarw. the heat-radiating inner heat exchanger 133.fwdarw. the receiver 136.fwdarw. the expansion valve 134.fwdarw. the heat-absorbing inner heat exchanger 135.fwdarw. the compressor 131. Accordingly, the outer heat exchanger 138 discharges heat of the refrigerant into the atmosphere, and the air led by the fan blower is cooled by the heat-absorbing inner heat exchanger 135 so as to supply conditioned-air for cooling into the passenger compartment.
With this air conditioner, during heating operation, the three-way valve 132 is switched as shown by the continuous line arrow so as to prevent the refrigerant from flowing into the outer heat exchanger 138 by means of the three-way valve 132 and the one-way valve 170. However, when the automotive vehicle equipped with such air conditioner is put in a cold district in winter, the outer heat exchanger 138 is largely chilled and therefore the refrigerant in the outer heat exchanger 138 changes its condition from a gas phase into a two-phase or liquid phase. Accordingly, the inner pressure of the outer heat exchanger 138 is decreased due to the increase of the density of the refrigerant. In almost all cases during the heating operation, the refrigerant in the system flows so as not to enter the outer heat exchanger 138 by means of the three-way valve 132 and the one-way valve 170. However, it may happen that the refrigerant is gradually flowed into the outer heat exchanger 138 according to the lowering of the inner pressure through a clearance of the three-way valve 132 or the one-way valve 170 which is formed by some reasons. If stagnation of refrigerant is generated in the outer heat exchanger 138 due to the entering of the refrigerant, the lack of refrigerant in the heat-pump cycle is caused and therefore the air conditioner is prevented from stably implementing the heating operation. Further, although it is possible to put the outer heat exchanger 138 into an unventilated condition by closing an air inlet of the outer heat exchanger 138 or to enlarge the volume of the receiver 136, such modulations tend to increase weight and production cost thereof.